The invention relates to a fan propeller comprising a boss and blades that extend radially outwards from the boss, the boss being suitable be fixed to the shaft of a motor so as to allow the motor to transmit a power of at least 150 watts to the propeller.
Such propellers are used in particular for the cooling of the driving engine of automotive vehicles, the propeller producing a flow of air through a cooling radiator.
It was assumed until now that the aeraulic and acoustic performances of such blades are better because their diameter and their axial length are greater.
As the available space in the engine compartment of vehicles is generally very limited, it is desirable to have cooling propellers of reduced spatial requirement, in particular in the axial direction.
Surprisingly, it has been discovered that, for a given diameter, the aeraulic and acoustic performances in practice only deteriorate beneath a certain optimal axial length.
The invention relates in particular to a propeller of the type defined in the introduction, and specifies that its axial length L, measured in metres, is not appreciably higher than the value L0 given by the following formula (I):
L0=0.426262xe2x88x925.14288.D+23.1798.D2xe2x88x9244.2505.D+30.8841.D4,
D being the diameter of the propeller measured in metres.
At least for certain geometric configurations of the blades, it is preferable for L not to be appreciably less than L0, as beneath this value performances decrease.
The upward and, if necessary, the downward range of variation of L in relation to L0 is 20 %.
The above variations apply particularly when the geometric configuration of the propeller has at least some of the following characteristics:
The axial ends of the blades and of the boss that are turned downstream from the flow of air produced by the propeller are roughly contained in the same radial plane.
The trailing edge of the blades is entirely contained in the said radial plane.
The axial ends of the blades and of the boss that are turned upstream from the flow of air produced by the propeller are roughly contained in the same radial plane.
The radially outer ends of the blades are connected to one another by a collar.
The blades are roughly identical to one another and uniformly spaced in the circumferential direction along an angular pitch xcex2, the point situated halfway between the leading and trailing edges at the radially outer end being offset in relation to the corresponding point at the base of the blade, in the opposite direction to the direction of rotation of the propeller, by an angle xcex1 of between roughly one half and three quarters of the angular pitch. This relates to the case of propellers known as symmetrical propellers.
The leading and trailing edges of each blade are convex in the direction of rotation of the propeller, the point situated half way between them progressively moving to the rear of the axial plane containing its position at the foot of the blade, then progressively returning right into this plane, over a fraction of the radial span of the blade of between 20 and 70%, and progressively moving forwards away from this same plane over the remaining fraction.
The acute angle xcexa9 between the chord of the flattened cross section of a blade and a radial plane decreases progressively at least over the last 30% of the radial span of the blade.
The boss comprises a roughly cylindrical wall from which the blades extend, and a base wall disposed substantially along a radial plane, turned downstream from the air flow produced by the propeller, the cylindrical wall and the base wall being connected to one another by a convex curved portion having a radius of curvature of between 4 and 8 mm.
The rounded portion roughly has a contour like a quarter of a circle with a radius of 5 mm.
The blades extend over the whole axial length of the cylindrical wall of the boss.
The boss is hollow and internally has ribs.